Q: 2009 Toyota Sienna, runs fine, fluids full, no heat inside vehicle, causes?

Hi there. It sounds like the air mix servo for the temperature control may have failed. These models were also prone to radiator and water pump leaks. The leaks would be slow and not produce fluid on the ground; sometimes the recovery bottle would still appear full. A good visual inspection of the radiator and water pump may reveal whether or not there is a coolant leak in these areas. There is also the possibility of the engine valley plate leaking coolant; the coolant puddles in the valley and does not leak to the ground making it a little more difficult to detect visually. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several technicians available that can assist you with a heater does not work inspection.